The invention of this application relates to methods of performing heart surgery. More particularly, this invention relates to that aspect of coronary artery bypass surgery which is concerned with the choice of arteries to be bypassed.
During coronary artery bypass surgery, the surgeon must make certain decisions about which arteries should be bypassed. Presently, two factors play the primary role in determining the choice of arteries to be bypassed. First, the cardiac catheterization studies before surgery provide information that assists in this decision-making process. After coronary arteries are injected with radiopaque dye, the arteriogram demonstrates which arteries are narrowed and the relative extent of that narrowing. Second, the physician must use his or her experienced judgment about the feel and size of the arteries at the time of surgery. Hard-walled arteries and very small arteries are less likely to be successful graft recipients than soft-walled and larger arteries.
There are short-comings in relying primarily on these two factors. These factors are based on structural considerations rather than upon blood flow and functional considerations. For example, obstructions which are present in primary and secondary branch arteries may not be demonstrated by the arteriogram. This condition can exist in advanced coronary artery disease as well as in diabetics, and also in areas of the heart which have been damaged by heart attacks. Not recognizing these obstructions can lead to inadvertent incomplete revascularization despite technically satisfactory grafts into apparently adequate coronary arteries. Additionally, the presence of small "collateral" arteries can similarly go undetected. Sufficient size and numbers of these small "collateral" arteries can make additional grafts of the large arteries unnecessary. In general, the present determinants are static factors applied to an operative procedure which has dynamic parameters from a medical perspective.
The long-term patency of bypass grafts has been known to depend primarily upon three factors: (1) the head of blood pressure, (2) technically satisfactory grafts and anastomoses, and (3) a good run-off bed.
In coronary bypass grafting, the head of blood pressure always comes from the aorta or one of its main branches, since this is always the best available head of pressure, and, therefore, depends upon the condition of the aorta and its main branches. The adequacy of the grafts and the anastomoses is a result of the skill of the physician. While the skill factor is ultimately determined on a surgeon-by-surgeon basis, it can be generally be assumed that today's highly skilled surgeons in a competitive atmosphere produce generally uniformly good grafts and anastomoses. Because these first two factors largely are predetermined, it can be said that the long-term patency of bypass grafts depends upon the remaining factor, the run-off bed.
It is known that grafts carrying a low flow of blood will very likely clot, and that grafts carrying a high flow of blood will very likely remain patent. Surgeons have been unable adequately to measure the flow requirement of a coronary run-off bed prior to the implantation of a bypass graft. Once a bypass graft is placed and functional, it is at that time possible to estimate the flow requirement of the coronary run-off bed by measuring the flow of blood through the graft with a flow meter. It would be useful to be able to estimate the flow requirement prior to placing a graft, however.
In elective coronary bypass surgery, an attempt is often made to place grafts into all vessels with significant proximal stenoses. Sometimes jump grafts are placed into the same vessel for multiple significant stenoses. In emergency bypasses, sometimes only the most significant stenoses are bypassed, and knowledge of the dynamic flow characteristics in the heart region is incomplete because the patient's condition mandates prompt surgery and the cessation of further studies.
In all of these circumstances, the surgeon must make decisions based on angiographic estimates of restriction of blood flow due to severity of areas of arterial narrowing without knowledge of some other useful and important factors. Some of the factors which the surgeon would not have knowledge of include severity of flow restriction by an area of narrowing, collateral flow of blood from neighboring arteries, shared perfusion beds, or, in some cases, even the status of the remaining arteries. Knowledge of shared perfusion beds is important because placement of competing grafts may endanger the outcome of surgery by jeopardizing the survival of an original graft as well as the competing graft. Also, jump grafts are technically more difficult to perform and are more likely to fail than simple grafts and are, therefore, to be avoided, if possible. Likewise, in some emergency situations, there is insufficient time to perform complete angiography which could indicate the need for further bypass grafts.
In many cases, thermal imaging may help in achieving a thorough revascularization in the shortest time of total cardiopulmonary bypass and with the greatest chance of long-term patency by providing useful and important information that permits the elimination of technical problems with anastomoses and competition of grafts in low flow situations.
The invention disclosed herein comprises a method of performing heart surgery which facilitates decision-making of the surgeon at the operating table by providing non-invasive, on-line information about dynamic variables of concern.